The tip and tilt M5 mirror of the European Extremly Large Telescope (E-ELT) requires a demanding approach in light weighting. The approximately 3 m x 2.5 m elliptical plano mirror is specified to a weight of less than 500 kg with high Eigenfrequencies and low deformation under different inclination angles. In 2011 SCHOTT has presented a study to develop a design for the M5 mirror blank of the ESO E-ELT. The design presented was based on a radial square design to achieve the best compromise between performance and manufacturability. With the fabrication of a prototype section SCHOTT demonstrated its capability to manufacture the demanding features including pockets with 350 mm depth, thin walls and sloped pocket bottoms. Now 3 years later SCHOTT presents an iso-grid based design that is in accordance with the manufacturability progress that has been demonstrated in various ELZM (Extremely Lightweighted ZERODUR Mirrors) publications in the last two years. The achievements on the specified mechanical parameters are compared to the first approach from 2011. In this paper the results are presented and the performance parameters are discussed.

Date Published: 18 July 2014
PDF: 11 pages
Proc. SPIE 9151, Advances in Optical and Mechanical Technologies for Telescopes and Instrumentation, 91510H (18 July 2014); doi: 10.1117/12.2054929

Published in SPIE Proceedings Vol. 9151:
Advances in Optical and Mechanical Technologies for Telescopes and Instrumentation
Ramón Navarro; Colin R. Cunningham; Allison A. Barto, Editor(s)